This invention pertains to electrostatic printing machines and more particularly to an improved toner fountain and recovery system for same.
In general, in electrostatic printing machines, an elongate web of material is moved in a predetermined path where, at one station, portions of the surface of the web will be electrostatically charged and thereafter developed in response to application of toner material thereto. Accordingly, the web typically is passed in close proximity across the top of a toner fountain in which liquid toner is overflowing the side edges thereof into a catch basin and returned to a reservoir.
One example of such a toner fountain is shown in U.S. Pat. No. 3,729,123, issued Apr. 24, 1973.
In apparatus of the kind described, the printing web is wetted as it is drawn across the toner fountain. Means are provided for physically removing first the bulk or main portion of the liquid toner and then the remainder.
As disclosed herein, however, vacuum means operating with a degree of suction determined by the hydraulic head required to pump liquid into the toner fountain has been utilized to recover the remainder portion of the liquid toner and to direct it to a toner reservoir.